SEPTEMBER 10, 1897.] 
habits of the species. Even then there may 
be danger, as with a new environment habits 
frequently change in a marked degree. 
b. Accidental introductions. The agency of 
man, however, has been more potent in ex- 
tending the range of species and in chang- 
ing the character of the faunas and floras 
of the regions which he inhabits by means 
of accidental importations. 
The era of accidental importations began 
with the beginning of commerce and has 
grown with the growth of commerce. The 
vast extensions of international trade of 
recent years, every improvement in rapidity 
of travel and in safety of carriage of goods 
of all kinds, have increased the opportuni- 
ties of accidental introductions, until at 
the present time there is hardly a civilized 
country which has not, firmly established 
and flourishing within its territory, hun- 
dreds of species of animals and plants of 
foreign origin, the time and means of in- 
troduction of many of which cannot be ex- 
actly traced, while of others even the origi- 
nal home cannot be ascertained, so wide- 
spread has their distribution become. 
These accidental importations would at 
first glance seem to have been more abun- 
dant with plants than with animals, since 
the opportunities for the carriage of seed, 
especially flying or burr-like seed, and es- 
pecially when we consider the vitality of 
this form of the plant organism, are plainly 
manifold, but I shall later show that pos- 
sibly even this obvious generalization must 
be modified in view of the multitudinous 
chances for free travel which the smaller 
insects have under our modern systems of 
transportation. 
The agencies which have mainly been in- 
strumental in the accidental distribution of 
plants are: 
1. Wind storms. It is obvious that light 
flying seeds may be carried many hundreds 
of miles by hurricanes and may fall in new 
regions. 
SCIENCE. 
385 
2. Water. This is a very important 
agency in the distribution of plants upon 
the same continent, but less important as 
affecting intracontinental distribution. Still 
they may be carried by this means from one 
island to another adjoining island, and when 
lodged in the crevices of the driftwood they 
undoubtedly travel greater distances. 
3. Birds. Seeds are frequently carried 
great distances by birds. Many of the 
larger seeds will germinate after passing 
through the alimentary canal of a bird, and 
- may thus be eaten at one point and voided 
with the excrement at a widely distant 
point. Ithas been shown, for example, that 
the local distribution of Rhus toxicodendron 
is greatly affected by the carriage and dis- 
tribution of the seed in this way by the com- 
mon crow. Smaller seeds are carried in 
earth on the feet of birds. Darwin’s ex- 
ample of a wounded red-legged partridge 
which had adhering to its leg a ball of earth 
weighing 64 ounces, from which he raised 
32 plants of about five distinct species, is an 
evidence of the possibilities of this agency, 
while his experiment with 6? ounces of mud 
from the edge of a pond which produced 537 
distinct plants, an average of a seed for every 
6 grains of mud, is still more conclusive. 
4. Ballast. This is the first of the distri- 
bution methods which may be combined 
under the head of ‘agency of man.’ The 
discharge of earth ballast by vessels com- 
ing from abroad has been a notable means 
of distribution of plants by seed. We have 
just seen how many seeds may germinate 
from a very small lump of earth, and the 
possibilities in this direction of the many 
thousands of pounds of discharged ballast 
are very great. In fact the ballast grounds 
in the neighborhood of great cities are in- 
variably favorite botanical collecting spots; 
they have usually a distinctive flora of their 
own, and from these centers many intro- 
duced plants spread into the surrounding 
country. 
